I'm confused about this pattern instructions. I'm knitting armhole & neck for left front v- neck cardigan but don't know how to decrease stitches as per below :

Bind off 4 sts at the beginning of next row, work to last 10 sts - k2 tog, (p1 k1) 8 times. Keeping pattern, continue to dec 1 sts as established every other row 4 more times then every 4th row 11 times.

It sounds like you're working each shoulder separately. BO 4 st at the armhole edge, then do the dec when there's 10 sts left and p1 k1 for 8 sts (not 8 times). Then turn and work a WS row, and dec the same on the next RS row - work to the last 10 sts - k2 tog, p1 k1 for 8 sts. when you've done 4 dec rows, then switch to doing the dec every 4th row instead of every other row 11 time.